The present invention relates to a draft force sensor for a towed or drawn implement, such as a drawn scraper.
Certain commercially available drawn scrapers are pulled by a towing vehicle, such as a tractor, and have tongue which is coupled to the towing vehicle. Scraper draft force or load is transmitted to the towing vehicle through the tongue. It is believed that scraper productivity and performance can be improved if the scraper draft force is controlled. This requires force sensors to sense the scraper draft force.
It has been attempted to sense or measure the draft load of a drawn scraper using load pins, load cells, and other methods. However, a load pin at a scraper pivot will experience wear with scraper use. The wires from a load pin would be exposed and subject to damage. Such a draft force sensor must also be sensitive to forces acting along a fore-and-aft direction and insensitive to forces acting in other directions.
U.S. Pat. No. 3,246,701 discloses a tractor hitch control system with electronic draft force sensing. Draft forces are sensed by strain gauges mounted on the walls of bores in each of the left and right hitch lower draft links. Such an arrangement of draft links and sensor bores is not suitable for the coupling of an implement such as a scraper where the implement is coupled through a single pivot/tongue coupling. Also, with single bores in each draft link, the strain gauges are sensitive to bending of the draft links, rather than only to draft forces transmitted along the main axis of the links.